The present invention relates to video picture analysis, and more particularly to a display format for viewing gamut errors in video pictures being analyzed.
Color video pictures may be represented in several different formats at different times during video processing. The color video pictures may be in an analog composite format, such as NTSC or PAL, in an analog component format, such as Y, Pb, Pr, in a digital component format, such as SMPTE 125M, in a primary color format, such as RGB, etc. In the course of processing the color video pictures there may be several conversions between the different formats. Each format has a different color space so that it is possible to produce colors in one format that are not reproducible in another format. The inability to reproduce a particular color from one color format in another color format is known as color gamut error.
Additionally analog composite signals usually have certain limits imposed on them for the proper operation of the broadcasting or receiving circuits. Composite signals that exceed a specified signal limit are referred to as having signal limit errors. For simplification color gamut and signal limit errors are referred to as gamut errors herein.
One method of detecting gamut error is disclosed in U.S. Pat. No. 4,707,727 where a color television signal in one format, such as component analog, is converted into a display format, such as primary color. The amplitudes of each component are compared with respective high and low thresholds such that, if either threshold is crossed, an error indication is generated. Such indication may be displayed simply as a light on a panel, or as a blanking, cross-hatching or false coloring on a display. The error indication may also be used to initiate a color correction of the pixels generating the error indication to bring the color of the pixels within gamut, i.e., within the reproducible colors of the new color space. The QA100 quality analyzer manufactured by Pinnacle Systems, Inc. of Mountain View, Calif., originally designed and manufactured by Hewlett-Packard of Palo Alto, Calif., is an example of the use of false coloring of any out-of-gamut pixels, while the WFM700 waveform monitor manufactured by Tektronix, Inc. of Beaverton, Oreg. is an example of overlaying a cross-hatch pattern across out-of-gamut pixels. Both of these methods overlay across normal full color video, and hence make it difficult to see if the gamut error occurs where there is a lot of color, motion, edges, etc., or if the gamut errors themselves occur in small patches.
What is desired is a display of gamut errors that doesn't hide the underlying video picture so it is easier to analyze the cause of the gamut errors.